1. Field of the Invention
The present invention relates to a permanent electrical contact applicable to the web or flange of rails and the like.
2. Description of the Related Art
As known, permanent electrical contacts for the electrical connection of sections of rail are required to have contact characteristics which reduce contact resistances and need to be structurally simple and robust. To such purpose, it is known to make permanent electrical contacts applicable to the web of a rail, by means of a bush in electrically conductive material having a cylindrical stem insertable in a hole made in the web of the rail and a flanged head suitable for engaging in abutment with the portion of rail surrounding the hole, wherein the bush has an axial through hole into which a punch can be inserted to generate a radial expansion of the cylindrical stem against the hole in the rail. Given its excellent mechanical characteristics (plastic deformation capacity and close engagement with the inner surface of the hole during the drawing of the material by means of the punch, elevated mechanical resistance and toughness) and electrical characteristics (high electric conductivity and electrogalvanic compatibility with steel), as well as its high resistance to corrosion, copper has up to today been the natural choice for making the contact bushes.
However, on account of the significant increase in the cost of copper and consequent frequent theft of conductors made from such metal, over recent years the use of electric conductors and connectors (so-called cable terminals) in aluminium has increased, the use of which however entails exposure to the environment of metals with different galvanic potential, such as copper and aluminium, with consequent risks of interstitial galvanic corrosion in the contact area between the aluminium connector and the contact bush in copper.
In order to overcome the problem of galvanic corrosion which could occur in the contact area between the aluminium and the copper, bi-metal connectors are currently sold on the market having a hollow seat in aluminium suitable for being compressed onto the conductor, as well as a terminal connection portion made of copper suitable for being connected in contact with a terminal, in which the hollow seat and the terminal connection portion are welded to each other.
Such solution, while resolving the problem of interstitial corrosion of the cable terminal in a satisfactory manner, is not without drawbacks. The manufacturing process of the single parts in aluminium and copper and their subsequent joining by welding is, on the one hand, complex and costly and, on the other, is not able to obtain a sufficiently reliable and resistant copper-aluminium connection for applications in which the connectors are subject to vibrations.